libcutils: add android_get_control_file()

am: 0b034d9d7b

Change-Id: I7d0a58c12839dba59aa43b96e5a920d3c415efcf

include/cutils/files.h

@@ -0,0 +1,37 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef __CUTILS_FILES_H
+#define __CUTILS_FILES_H
+
+#define ANDROID_FILE_ENV_PREFIX "ANDROID_FILE_"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/*
+ * android_get_control_file - simple helper function to get the file
+ * descriptor of our init-managed file. `path' is the filename path as
+ * given in init.rc. Returns -1 on error.
+ */
+int android_get_control_file(const char* path);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* __CUTILS_FILES_H */

libcutils/Android.bp

@@ -34,6 +34,7 @@ cc_library {
     host_supported: true,
     srcs: [
         "config_utils.c",
+        "files.cpp",
         "fs_config.c",
         "canned_fs_config.c",
         "hashmap.c",

libcutils/files.cpp

@@ -0,0 +1,111 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+// This file contains files implementation that can be shared between
+// platforms as long as the correct headers are included.
+#define _GNU_SOURCE 1 // for asprintf
+
+#include <ctype.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <cutils/files.h>
+
+#ifndef TEMP_FAILURE_RETRY // _WIN32 does not define
+#define TEMP_FAILURE_RETRY(exp) (exp)
+#endif
+
+int android_get_control_file(const char* path) {
+    if (!path) return -1;
+
+    char *key = NULL;
+    if (asprintf(&key, ANDROID_FILE_ENV_PREFIX "%s", path) < 0) return -1;
+    if (!key) return -1;
+
+    char *cp = key;
+    while (*cp) {
+        if (!isalnum(*cp)) *cp = '_';
+        ++cp;
+    }
+
+    const char* val = getenv(key);
+    free(key);
+    if (!val) return -1;
+
+    errno = 0;
+    long fd = strtol(val, NULL, 10);
+    if (errno) return -1;
+
+    // validity checking
+    if ((fd < 0) || (fd > INT_MAX)) return -1;
+#if defined(_SC_OPEN_MAX)
+    if (fd >= sysconf(_SC_OPEN_MAX)) return -1;
+#elif defined(OPEN_MAX)
+    if (fd >= OPEN_MAX) return -1;
+#elif defined(_POSIX_OPEN_MAX)
+    if (fd >= _POSIX_OPEN_MAX) return -1;
+#endif
+
+#if defined(F_GETFD)
+    if (TEMP_FAILURE_RETRY(fcntl(fd, F_GETFD)) < 0) return -1;
+#elif defined(F_GETFL)
+    if (TEMP_FAILURE_RETRY(fcntl(fd, F_GETFL)) < 0) return -1;
+#else
+    struct stat s;
+    if (TEMP_FAILURE_RETRY(fstat(fd, &s)) < 0) return -1;
+#endif
+
+#if defined(__linux__)
+    char *proc = NULL;
+    if (asprintf(&proc, "/proc/self/fd/%ld", fd) < 0) return -1;
+    if (!proc) return -1;
+
+    size_t len = strlen(path);
+    char *buf = static_cast<char *>(calloc(1, len + 2));
+    if (!buf) {
+        free(proc);
+        return -1;
+    }
+    ssize_t ret = TEMP_FAILURE_RETRY(readlink(proc, buf, len + 1));
+    free(proc);
+    int cmp = (len != static_cast<size_t>(ret)) || strcmp(buf, path);
+    free(buf);
+    if (ret < 0) return -1;
+    if (cmp != 0) return -1;
+#endif
+
+    // It is what we think it is
+    return static_cast<int>(fd);
+}

libcutils/tests/Android.bp

@@ -14,7 +14,7 @@
 
 cc_defaults {
     name: "libcutils_test_default",
-    srcs: ["sockets_test.cpp"],
+    srcs: ["sockets_test.cpp", "files_test.cpp"],
 
     target: {
         android: {

libcutils/tests/files_test.cpp

@@ -0,0 +1,46 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <time.h>
+
+#include <cutils/files.h>
+#include <gtest/gtest.h>
+
+TEST(FilesTest, android_get_control_file) {
+    static const char key[] = ANDROID_FILE_ENV_PREFIX "_dev_kmsg";
+    static const char name[] = "/dev/kmsg";
+
+    EXPECT_EQ(unsetenv(key), 0);
+    EXPECT_EQ(android_get_control_file(name), -1);
+
+    int fd;
+    ASSERT_GE(fd = open(name, O_RDONLY | O_CLOEXEC), 0);
+    EXPECT_EQ(android_get_control_file(name), -1);
+
+    char val[32];
+    snprintf(val, sizeof(val), "%d", fd);
+    EXPECT_EQ(setenv(key, val, true), 0);
+
+    EXPECT_EQ(android_get_control_file(name), fd);
+    close(fd);
+    EXPECT_EQ(android_get_control_file(name), -1);
+    EXPECT_EQ(unsetenv(key), 0);
+    EXPECT_EQ(android_get_control_file(name), -1);
+}